As is well known to those skilled in the art, polyurethanes are prepared by reacting an organic polyfunctional polyisocyanate (typically an aliphatic isocyanate as in the case of coatings, a polymeric isocyanate as in the case of rigid foams, or a tolylene diisocyanate as in the case of flexible foams) with an organic composition having at least two Zerewitinoff active hydrogen atoms. Typical of these latter compositions are various polyesters, polyester amides, polyoxyalkylene polyols, polyoxyalkylene ethers, polyacetals, polyoxyalkylene thioethers, etc.
When the desired product is to be a non-foamed urethane elastomer, the reaction is conducted under anhydrous conditions and no blowing agent is added. When the desired product is topbe a foamed urethane, water and an excess of isocyanate may be added to the mixture; as the water reacts with the isocyanate groups, carbon dioxide is formed and this gas is entrapped within the reaction mixture. In addition (or alternatively) auxiliary blowing agents such as volatile Freons may be added.
When the foamed urethane is the desired product, it is common to add a blowing catalyst which regulates the water-isocyanate reaction. A common blowing catalyst is N-ethyl morpholine.
Common commercial practice includes the addition to either system of a gelling or gel catalyst which controls the reaction of the e.g. polyol and the isocyanate. In the case of the non-foamed elastomer urethanes, blowing catalyst is omitted and a gel catalyst is used.
It is found however that many of the prior art gel catalysts are undesirable in that they are characterized by undesirably high level of toxicity together with attendant ecological disadvantages. Another disadvantage of prior art catalysts is their lack of specificity: i.e. although a particular prior art catalyst may be commonly considered to serve as a gel catalyst, in fact it also serves to catalyze the blowing reaction. This is undesirable in that it proscribes the desired independent control of the gelling reaction and the blowing reaction. In the case of non-foamed urethane elastomers in particular, it is found that gel catalysts heretofore tried undesirably possess sufficiently high blowing catalytic ability so that they catalyze the reaction between isocyanate and trace quantities of water in the system, to give products characterized by an undesirable degree of blowing. In practice, this is observed as undesirable bubbles in a urethane elastomer product.
Although attempts have heretofore been made to provide gel catalysts which possess little or no blowing ability, commercial practice has been to attempt to produce elastomers from dry charge materials which latter meet severe requirements with respect to water content.
It is an object of this invention to provide a novel process for preparing urethane polymers. Other objects will be apparent to those skilled in the art from the description which follows.